This invention relates to a coolant purification system and more particularly to an improved apparatus for removing foreign particles from the cooling and lubricating fluid used in machining operations.
In many types of machine operations, a coolant is supplied to the area being machined for a number of purposes. One of these purposes is to cool and lubricate the machining operation. The other and equally important purpose is to remove the machined particles as well as other foreign matter from the area where machining is occurring so as to improve surface finish.
Although in principle this appears to be simple and obvious, accomplishing these results and being able to operate the equipment over long periods without servicing presents substantial considerations. Environmental concerns also require the reclaiming of the coolant and lubricant and recirculation of it, and this adds greatly to the aforenoted problems.
In some ways, this invention relates to an improvement or an alternative arrangement for providing coolant purification to that shown in my copending United States Letters Patent of the same title, Ser. No. 09/063,017 filed Apr. 20, 1998, now U.S. Pat. No. 6,015,487, and assigned to the assignee hereof.
A prior art type of apparatus is illustrated in FIG. 1 and the effectiveness of various types of prior filtering materials utilized for coolant purification is shown in FIGS. 2 and 3. The apparatus shown in FIG. 1 includes a machining station 21 having a cutting tool 22 that operates to machine the surfaces of a work piece 23. In the illustrated embodiment, by way of example, the cutting tool 22 is a grinding wheel and the work piece 23 is a gear blank onto which gear teeth are formed by the grinding operation.
This grinding operation takes place over a catch tank 24 with a coolant supply nozzle 25 being provided so as to spray the cooling liquid to the machined area. This liquid is then collected in the catch tank 24 and is returned to a purification apparatus, indicated generally by the reference numeral 26, where the cutting liquid is collected in a storage tank 27. A pump 28 draws the coolant from the storage tank 27 and delivers it via the nozzle 28 to the machine area.
In the specific prior art example shown, the purification apparatus 26 comprises a centrifugal separator including an impeller element 29 that is driven by an electric motor 31 and which separates foreign particles from the coolant in a manner known. The purified coolant is returned to the storage tank 27 through a purification return line 32.
FIG. 2 shows the typical efficiency of this type of centrifugal apparatus by indicating the NAS value. This NAS value is a standard by which the number and size of entrain particles captured by the filter are measured. On the absissa, the size of particles is shown, while on the ordinate, the NAS number is indicated.
It will be seen that the centrifugal type separator is fairly consistent in the NAS number of the particles of varying sizes, but nevertheless does not exclude as many particles as desired, particularly those in the larger sizes, such as 50-100 .mu.m. Thus its efficiency is not great.
Another type of filter which may be employed for purifying coolant and which has a higher filtration efficiency is the diatomaceous earth type. FIG. 3 shows the efficiency of this type of filter.
As may be seen in this figure, the efficiency is higher, particularly with larger size particles. However, this type of filter requires frequent servicing and hence is expensive to operate and does not afford long operational cycles between servicing. Also, the smaller size particles are more difficult to capture with this type of filter if reasonable flow velocities and small size of the filter are obtained.
Therefore, it is a principle object of this invention to provide an improved coolant purification system usable with machining operations that will remove with high efficiencies particles of a variety of sizes and which can be operated for long time intervals without necessitating servicing.
It is a principle object, therefore, to provide an improved coolant purification system for a machining apparatus that has high efficiency and long service life while permitting operation at lower cost.